1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus for performing imaging of organs and so on within a living body by transmitting and receiving ultrasonic waves to generate ultrasonic images to be used for diagnoses.
2. Description of a Related Art
In an ultrasonic diagnostic apparatus to be used for medical application, normally, an ultrasonic probe including plural ultrasonic transducers having transmitting and receiving functions of ultrasonic waves is used. An object to be inspected is scanned by an ultrasonic beam transmitted from the plural ultrasonic transducers and the ultrasonic echoes reflected within the object are received, and thereby, image information on the object tissues is obtained based on the intensity of the ultrasonic echoes. Further, information on blood movement within the object can be obtained based on frequency shift information due to the Doppler effect contained in the ultrasonic echoes.
Currently, as a method of obtaining a real blood flow velocity, as shown in FIG. 5, real blood flow velocity “V” is calculated based on velocity component “Vy” in a sound ray direction obtained according to the Doppler effect by calculating an angle (Doppler angle) “θ” formed by the sound ray direction and the blood flow direction. For example, the real blood flow velocity “V” can be calculated using the following equation.V=Vy/cos θHowever, near the location where the Doppler angle θ is 90°, an error of the calculated blood flow velocity “V” becomes greater, or it becomes impossible to obtain the blood flow velocity “V”.
As a related technology, Japanese Patent Application Publication JP-A-5-115479 discloses an ultrasonic diagnostic apparatus aimed to obtain two dimensional blood flow velocity and amount of tissue displacement with high accuracy in real time, and to obtain signals having intensity according to the reflection intensity even when ultrasonic waves are diagonally reflected. The ultrasonic diagnostic apparatus includes plural weighted addition means for setting directions of reception beams to directions different from one another, and obtains components of the blood flow velocity and/or amount of tissue displacement in the directions of the respective reception beams based on the respective added signals and combines these line segments to obtain and display the blood flow velocity and/or amount of tissue displacement as two-dimensional vector quantities.
Further, Japanese Patent Application Publication JP-P2005-110939A discloses an observation apparatus aimed to obtain the state of the flow within an observation surface that is reasonable to some degree in practice under a constraint that only information on a beam direction velocity component obtained by the Doppler method using a single beam can be obtained. The observation apparatus calculates a flow rate function by integrating a beam direction velocity component at the respective points obtained by the Doppler method along the path orthogonal to the beam, obtains an integration value of only positive values and an integration value of only negative values of the beam direction velocity component along the path, considers the smaller one of the integration values as a flow rate of vortex, obtains the velocity component of the vortex in the beam direction from the ratio of the flow rate of vortex to the larger one of them, calculates a flow function of vortex by considering the vortex as a two-dimensional flow, and further, calculates the velocity component of the vortex in the direction orthogonal to the beam from the flow function.
However, in JP-A-5-115479 and JP-P2005-110939A, the correction based on the angle is performed on the respective velocity components obtained by the Doppler method, and therefore, the calculated blood flow velocity has angle dependence. That is, calculation is impossible when the Doppler angle is 90°, and the result is not the real blood flow velocity. Further, other methods of obtaining the real blood flow velocity using a two-dimensional array probe or a cross beam system are considerable, but the methods are impractical because large-scaled apparatuses are necessary therefor.